1. Field of the Invention
This invention relates to an apparatus for controlling inlet air flow in an internal combustion engine, and more particularly, to such an inlet air flow control apparatus in an engine having a turbo-supercharger.
2. Description of the Related Art
A known type of inlet air flow control device for an engine having a turbo-supercharger is disclosed in Japanese Unexamined Utility Model Publication 59-119943. This device comprises a first air inlet means connected via a first intake valve to a combustion chamber and a second air inlet means connected via a second intake valve to the combustion chamber, both the first and second air inlet means being connected to an air compressor of the turbo-supercharger; and an inlet air flow control valve provided in the second air inlet means, which operates in response to the compressed air pressure, i.e., the inlet air flow control valve is fully open when the compressed air pressure exceeds a predetermined value.
That is, when the engine revolutional speed is relatively low, the turbo-supercharger does not effect an air supercharging operation and, therefore, the air pressure at an intake port is low. In this condition, the inlet air flow control valve is closed so that inlet air passes only through the first air inlet means. Therefore, the flow of the inlet air is maintained at a high speed so that it is possible to supply the inlet air at a high flow speed into the combustion chamber through the inertia of the inlet air itself. On the other hand, when the engine revolutional speed is relatively high, the turbo-supercharger effects an air supercharging operation and, therefore, the inlet air flow control valve is opened in response to the pressure of the air. In this condition, the compressed inlet air passes through both the first and second air inlet means, so that it is possible to obtain a high engine output power.
In a known inlet air flow control device as mentioned above, in an accelerating transitional condition of the engine, as the inlet air flow control valve remains open until the pressure of the compressed air reaches a predetermined value, the flow speed of the inlet air is increased due to the effects of the inertia of the inlet air itself. Accordingly, to make the most effective use of the inertia of the inlet air, the inlet air flow control valve should remain closed until the engine revolutional speed reaches a predetermined value. However, in an accelerating transitional condition of the engine there is an abrupt increase of the inlet air flow speed, and accordingly, knocking will occur and cause a loss of engine torque, which results in a reduced inlet air flow speed and a delay in the time at which the turbo-supercharger has an effect, thus affecting the acceleration response of the engine.